1. Field of the Invention
The field of art to which the invention pertains includes the filed of segment measuring devices for spectacle lenses, particularly with respect to a measuring gauge which is self-retaining when inserted into the lens well of a frame.
2. Description of the Prior Art
In order to determine bifocal lens segment size and placement for lenses within the lens frames, a standard millimeter rule has been used to estimate the approximate position of bifocal segments for conveying this information to the lens maker. This approximation technique has been proven inaccurate. One type of an arrangement to improve this accuracy includes a transparent lens segment which is provided with a scale. The narrow lower end is positioned in the lens well of the lens frame and a resilient member is secured to the lens segment. The resilient member engages the upper portion of the lens frame for releasably securing the lens segment in the roof of the frame. Typically, the resilient member is a spring which is attached to the lens segment. It has been found, particularly with the use of oversized frames, that the spring and lens segment combination would slip thereby causing the scale to be displaced at an angle and thus giving an inaccurate reading. In addition, different sized lens segment and spring arrangements must be stocked for different sized frames. Further, the measuring device must be inverted to permit determination of the most desirable and functional placement of the upper segment in double segment bifocals.
The present invention overcomes the prior art disadvantages of the lens segment and spring combinatins as well as other prior art devices and is formed of a relatively inexpensive unitary gauge. The measuring gauge can be utilized with all sizes frames and gives an accurate reading of the proper lens segment.
Known prior art includes U.S. Pat. Nos. 1,675,407; 1,981,438; 2,326,030; and 2,632,257.